Wireless electrical power transfer systems, such as those used for wireless charging, are known to incorporate a first coil structure, hereafter referred to as a source coil, that includes a tuned resonant circuit that is configured to convert alternating electrical energy from an electrical power supply to a magnetic field and to transfer the magnetic energy via the magnetic field to a spaced apart second coil structure, hereafter referred to as a capture coil. The capture coil also includes a tuned resonant circuit configured for receiving the magnetic field and converting the magnetic field to electrical energy that is supplied to an electrical load, such as a battery pack or motor. Such a wireless power transfer system may be used for electrically charging an energy storage device, such as the battery pack of an electric or hybrid electric vehicle. In such a system, the source coil may be located on, or embedded into, a surface beneath the vehicle, e.g. the floor of a garage or the surface of a parking lot, and the capture coil may be disposed on the underside of the vehicle.
The current and voltage of the electrical power supplied by the capture coil is determined by the voltage of the electrical power supplied by the power source to the source coil. A control system incorporating feedback of the capture coil voltage and current may be used to control the voltage of the electrical power supplied by the power supply. In order to maintain a wireless connection between the power source and the capture coil, typically the operation of wireless vehicle charging systems has depended primarily on a feedback loop that operates through a wireless communication channel, commonly a wireless channel conforming to Institute of Electrical and Electronics Engineers (IEEE) specification 802.11 (often referred to as “Wi-Fi”). The wireless communication results in a “sampling” effect in the data feedback. The wireless channel also introduces highly variable delays (beyond that of the sampling) and packet losses that require retransmission of the data (another source of delay). The effects of this delay (and its destabilizing effect on the control loop) restricts the possible control bandwidth for the closed-loop control. The control system then does not respond quickly enough to disturbances in the system to ensure reliable operation.
The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also be inventions.